In commonly assigned U.S. Pat. No. 4,977,419, a photographic filmstrip having a virtually transparent, magnetic film layer on the non-emulsion side of the filmstrip (referred to as an MOF layer) is disclosed for use in camera systems. One or more longitudinal read/write tracks are illustrated in the MOF layer between the side edges of the image frame area and the filmstrip where information such as film type, film speed, film exposure information and information relevant to the processing and subsequent use (e.g., printing) of the exposed image frames is pre-recorded during manufacture of the filmstrip cartridge. The pre-recorded information useful for controlling camera operations may be read out in a camera, and information related to the exposure of an image frame may be recorded in certain other tracks during camera use. The information recorded during camera use may include voiced messages or sound associated with the photographed scene and may be recorded in digital or analog format on the certain tracks. It is contemplated that both the pre-recorded and the camera use recorded information will be read out for control and reprint purposes during photofinishing. Also, it is contemplated that the photofinisher may have the capability to record additional information related to finishing, e.g. printing exposure conditions, customer information, reorder information, etc., in further tracks.
Referring now to FIG. 1, the MOF layers on a film strip 10 in which such information may be recorded and from which pre-recorded information may be read out are depicted. The magnetically coated color negative 35 mm film strip 10 includes a base 11, various well-known photo-chemical emulsion layers 13 on one side of the base 11 and a virtually transparent MOF layer 15 on the other side. An anti-static and lubricating layer 17 overlies the MOF layer 15. The film strip 10 includes a single perforation 19 along at least one film edge at regular intervals matching the pitch of a metering pawl in a camera adapted to use the film strip 10.
For purposes of recording data in the magnetic layer 15, each three of the film strip 10 may be formatted as shown in FIG. 1 (as more fully described in the '419 patent, the disclosure of which is incorporated herein by reference). The frame area is divided into a plurality of predetermined longitudinal track locations designated in the drawing as outermost tracks C0-C3 and innermost tracks F00-F29. As described more fully in the '419 patent, certain of the tracks may be reserved for recording of information in the camera using magnetic recording means included in the camera. In addition, other tracks may be reserved tier use by the photofinisher, and certain of the tracks may be used for recording of audio information.
In filmstrip 10, first edge tracks C0 and C1 are formed in imperforate edge region 10a and second edge tracks C2 and C3 are formed in perforate edge region 10b. In order to accommodate the presence of the camera tracks C2 and C3 along the edge region 10b, the perforations 19 are spaced to be adjacent the borders of successive image frames. In the embodiment of FIG. 1, there is only one perforation 19 in each frame border along only the edge region 10b. However, it will be understood that two perforations adjacent the beginning and the end of each image frame may be provided in edge region 10b as described in the above-referenced '175 application.
The camera and photo finishing systems that have been proposed for recording and reading to or from the tracks F00-F29 employ elongated arrays of a multitude of magnetic heads, e.g. the array disclosed in the above-referenced '532 application. Moreover, a variety of magnetic head suspension and/or backing plate configurations have been proposed to ensure compliance with the MOF layer 15 while avoiding the scratching of the emulsion layers 13.
The photographic filmstrip 10 is of much greater thickness than the magnetic tape used for commercial and consumer recording and reproduction and is neither compliant nor inherently flat. When removed from its cartridge, such a filmstrip shows a relatively high stiffness and very observable cross-film curvature across its width that is convex on or toward the emulsion side of the filmstrip as shown in the illustration of FIG. 2. Further, the unwrapped filmstrip also shows a convex curvature along its length, again on the emulsion side of the film. This latter curvature is attributed primarily to a core-set curl that results from the filmstrip having been tightly wound on a film cartridge spool.
The cross-curvature or curl across the width of the filmstrip 10 is primarily caused by the number of emulsion layers 13 and the MOF layer 15. The emulsion and MOF layers have different stretch properties than that of the base film substrate of acetate, PET, or PEN material. The cross-film curvature is also influenced by the bending phenomena known as anticlastic curvature. The degree of cross-film curvature also depends on environmental conditions, including the time and temperature history of the film, the relative humidity, and the thickness of the film. The cross-film curvature that occurs in the film 10 can also result in "ears" formed at the edges of the film as it curls further inward as shown at 20 and 22.
In the photographic filmstrip 10 bearing the MOF layer 15 described above, the density of the virtually transparent MOF layer is much lower than in magnetic tape. Because of the low magnetic density of the MOF layer 15 and the susceptibility of the emulsion layers 13 to scratching and damage, it is of particular importance that the magnetic head-to-film interface must have high compliance and avoid scratching the MOF layer 15 or the emulsion layers 13. As a result, extreme care must be taken in the design of the components of the interface to ensure that a minimum of surface damage occurs at the magnetic head interface with MOF layer 15 and any load supporting member on the emulsion layer 13.
Because of the cross-film curl, it is difficult to achieve good contact or compliance across the width of a wide, multi-head array. To provide a reliable read or write signal, the length of the magnetic head gap must remain in close proximity to the magnetic coating. Any disturbances, such as variations in cross film curl, can vary the relationship of the magnetic head gap to the magnetic coating and decrease the reliability of the signal. Consequently, to provide high quality and reliability required for camera usage, such head arrays are relatively expensive.